A gas chromatograph/mass spectrometer at the Maryland State Police Forensic Sciences Division (FSD) laboratory. Gas chromatography is used in analytical chemistry for separating and analyzing compounds. Typical uses of gas chromatography include testing the purity of a particular substance or separating the different components of a mixture (the relative amounts of such components can also be determined). In some situations (such as forensic analysis) gas chromatography may help to identify an unknown compound found at a crime scene or determine the type and purity of illegal drugs.